Transmission fluid has nothing to do with the strength of it's internal components. What transmission are you using? FWD SR20DE transmissions have a weak input shaft bearing and gearset. I won't say there aren't a few lucky people that don't have problems, but this is mechanical knowledge. A heavy duty clutch, such as a puck setup, will also add to the problem. If you are going to make big power the input shaft bearing needs to be "beefed" and the gearset must be cryo-treated, or else boom...no 3rd gear.